1. Field of the Invention
The present invention relates to a multi-phase switching regulator, and more particularly to a switching regulator which performs control using a logic circuit.
2. Description of the Related Art
A switching regulator is used for many electronic devices. Generally a switching regulator converts input voltage into a predetermined voltage, and supplies it to circuits in the device.
FIG. 1A is a diagram depicting a configuration of a conventional switching regulator. FIG. 1B is a timing chart in the configuration in FIG. 1A. The conventional switching regulator comprises a differential amplifier 201, a reference voltage generation circuit 202, a comparator 203, a triangular wave generation circuit 204, a driver 205 and a transistor 206. The output voltage Vout of the conventional switching regulator is fed back to the differential amplifier 201. The reference voltage generated by the reference voltage generation circuit 202 is also input to the differential amplifier 201. The differential amplifier 201 compares the two inputs, and outputs an error voltage according to the comparison result.
FIG. 1B shows an error voltage VD by a dashed line. Along with the error voltage DV, a triangular wave TW, which is output from the triangular generation circuit 204, is input to the comparator 203. The comparator 203 compares the two inputs, and generates a PWM (Pulse Width Modulation) pulse.
Now the error voltage DV and the triangular wave TW in FIG. 1B will be described to assist in understanding the operation of the comparator 203. Here the time m0 to m7 is time when the error voltage DV and the triangular wave TW cross. In the period between time m0 and m1, the potential is lower in the error voltage DV than in the triangular wave TW. Therefore in the period between m0 and m1, the PWM pulse is at low level. In a period between time m1 and m2, the potential is higher in the error voltage DV than in the triangular wave TW. Therefore in the period between time m1 and m2, the PWM pulse is at high level. In the same manner, the high level and low level of the PWM pulse are switched at a time when the error voltage DV and triangular wave TW cross.
The generated PWM pulse is supplied to the driver 205, and the driver 205 supplies the signal RS, that is the inverted PWM pulse, to the gate of the transistor 206. The high level of the signal RS turns the transistor 206 ON. At this time, current It flows through the transistor 206. For example, the signal RS is at high level in the periods between time m4 and m5, and between time m6 and m7, and during these times the current It flows through the transistor 206, which is ON.
The current It is a current that flows from the input power supply Vin to the ground, and stores energy in the coil L which the current flow through. The amount of the stored energy is determined by the width of the PWM pulse. The energy stored in the coil L is supplied to an output terminal 207 as an output voltage at a timing when the driver 205 is not driving the transistor 206. The output power is supplied to an external circuit 208 via the output terminal 207. By adjusting this output power amount, the output voltage Vout in the output terminal 207 is maintained at a target voltage even if the load in the external circuit 208 fluctuates.
In such a switching regulator, if fluctuation of the load of the external circuit to which the output power is supplied is large, the adjustment width of the power to be supplied must be large as well. Therefore in this case, it is desirable to combine a plurality of switching regulators and supply the combined output power to the external circuit. Japanese Patent Application Laid-Open No. H4-210776 discloses a configuration using two switching regulators that are combined.
The switching regulator disclosed in Japanese Patent Application Laid-Open No. H4-210776 uses both a pulse width modulation type switching regulator and a resonance type switching regulator. In this switching regulator, only the pulse modulation type switching regulator operates in an area where the output power is low. At a point when the power to be output exceeds a predetermined value, the resonance type switching regulator is activated so as to increase the output power and maintain the target voltage.